Why is Europe so far ahead of the US in their re-thinking of urban environments? Maybe it’s because most of our cities grew up in the automobile era while Europe’s major cities have been around for millennia. But even that difference can’t explain why the best new green ideas come from Europe – take Madrid’s air tree for example.

The “tree” looks a bit goofy, like a giant glass hollow Slinkie. But don’t let its looks fool you. It’s designed to be a heat sink for major cities, providing cool places on ordinarily heat-absorbing stretches of pavement. It provides shade, and the air temperature differential creates a light breeze. It also provides free electricity to the grid (from an array of solar panels) and the real trees enclosed in the glass structure absorb CO2 and produce oxygen.

Another interesting design feature is that these trees are highly mobile They’re made of lightweight, recycled materials and can be moved around a city for feature events or to popular gathering places. Madrid plans to have trees placed all over the city in the next few years. Imagine if big concert promoters buy up a few.

Is the air tree the solution for future urban energy and heat problems? Probably not, but it certainly represents a futuristic, clean-energy attraction as a stop gap to cleaner cities.